120 PROCEEDINGS OF THE NATIONAL MUSEUM. 



each of the three most important economic species, TJirips tahaci, 

 Euthrijys trltici, and Anaphothrips striatus, has been experimented 

 with considerably. Webster recommends, for Thrh]}i< tahacl in the 

 field, spraying thoroughly with 1 pound of Standard w-hale-oil soap in 

 8 gallons of water (476), and he says also, "The grassy borders of 

 ditches have been sprayed with kerosene with excellent results." 

 Quaintance (454) tried many insecticides for Thrips tabaci and EutJirips 

 trltlci in Florida and found that "rose leaf insecticide"—! pint in s 

 o-allons of water— killed from 65 to 70 per cent of the insects, and was 

 the most successful of anything tested. For 77ir^>.^• tahacl he recom- 

 mends "whale-oil soap (Anchor brand), at the rate of 1 pound of 

 SOU]) to 4 gallons of water," or '■'•rose leaf insecticide at the rate of 1 

 pint to 4 gallons of water." 



Sprays must be very thoroughly applied to do even fair service, and 

 ditches and margins around fields, as well as the ground betw^een rows, 

 should ])e treated also. Even with the most careful treatment many 

 of the tiny insects will escape the spray, and the embedded eggs are 

 entirely unharmed. Therefore, spraying, to be at all successful, must 

 be repeated after a short interval. It must be admitted that at best 

 spraying is an unsatisfactory remed}'-; still, it is perhaps the best 

 method we know of at present for field work. 



In greeidiouses spraying may be more successful than in the field, 

 but fiunigation methods are here preferable. These also must be 

 repeated in about a week to be successful. The most satisfactory 

 results have here been ol>tained l)y the vaporization at night of ^0 cc. 

 of "Nikoteen" in 750 cc. of water for 5,000 cubic feet of space. This 

 treatment did not injure the cucumber plants, while nearly all of the 

 T/irtj).s tahacl were killed (471). 



Cultural methods. — These are undoubtedly too important to be 

 neglected, even if insecticides be used, and in some cases they may 

 prove even more efficient than the latter. For the Onion Thrips, Weli- 

 ster says: "All culls, tops, and other refuse of onion fields should l)e 

 burned in the fall." He also recommends the burning of the grass 

 along ditches and around the margins of the fields in winter or early 

 spring to destroy the hibernating insects (476). 



For the Grass Thi-ips it seems that cultural methods are the only 

 ones that can be of any considerable help. A thorough burning of 

 the old grass in early spring before growth begins destroys large 

 numbers of hibernating insects— Thrips and many others. The attacks 

 of the Grass Thrips are worst upon old, worn-out meadows, fields, and 

 lawns, largely because Poa jjratensls (June grass) is most common in 

 such places. Infested grass should be cut as early as possible or fed 

 green. So far as I can learn, the seed of June grass is sold only in 

 lawn mixtures and is not used for field seeding, though it comes in 

 naturally as the other stouter-growing species which are usually sown 

 run out. The appearance of a large amount of " Silver Top " is there- 



